The present invention relates generally to wireless networks, and more specifically to a system for detecting radar signals using dynamic frequency selection.
Wireless Local Area Network (WLAN) devices must coexist with radar in the 5 GHz frequency bands. Interference mitigation techniques are required to enable WLAN devices to share these frequency bands with radar systems. The general requirement is that these devices detect interference, identify the radar interfering sources, and avoid using the frequencies used by the radar. Dynamic Frequency Selection (DFS) is used as a spectrum sharing mechanism by certain standards committees that define rules dictating the use of the 5 GHz space. For example, the European Telecommunications Standards Institute (ETSI), which is involved in developing standards for Broadband Radio Access Networks (BRAN), requires that transceiver equipment for use in HIPERLAN (High Performance Radio Local Area Networks) employ DFS mechanisms to detect interference from other systems to enable avoidance with co-channel operations with these other systems, notably radar systems. The goal is to provide a uniform spread of equipment loading across a number of channels, such as fourteen channels of 330 MHz each, or 255 MHz each for equipment used only in bands 5470 MHz to 5725 MHz.
Present proposals from the ETSI BRAN committee provide various simple guidelines for radar detection. These include detecting and avoiding radar signals that only appear at a level above a certain pre-defined threshold, such as xe2x88x9262 dBm. In one implementation, detection is based on a simple algorithm to see whether there are any instances of signals above the xe2x88x9262 dBm threshold during a ten second startup listening period. Another proposed guideline is that detection during normal operation should be addressed by periodically suspending all network traffic and listening in startup mode for any instances of signals above the xe2x88x9262 dBm threshold level.
Despite the simple guidelines proposed by the present standards committees, the radar and satellite industries increasingly expect 5 GHz WLAN devices to detect radar signals during normal operation. Thus, WLAN stations will need to detect radar when they are both transmitting LAN packets, and when they are idle. This will increase the chance of quickly detecting radar sources that are passing through an area of operation of the WLAN device, and thereby reduce interference with such radar sources.
However, the present proposed methods of radar detection and avoidance within the 5 GHz space present certain disadvantages, especially in view of increased network traffic in the 5 GHz radio spectrum, and the need for increased bandwidth among WLAN devices. For the simple threshold check method proposed by the ETSI BRAN committee, a significant disadvantage is the possibility of detecting false positive readings if threshold levels for signal detection are set too low. Another disadvantage includes the inability to effectively distinguish overlapping cells that may be operating co-channel during a measurement period. Moreover, with regard to WLAN equipment operation, the requirement to detect radar signals during normal LAN operation by periodically suspending network traffic can place a significant burden on the processing and data transfer capacity of these devices.
What is needed therefore, is a system that efficiently and accurately identifies radar in a WLAN device, and allows the device to switch frequency channels without imposing an undue burden in traffic processing throughput. Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.